An image intensifier amplifies the photons reflected or emitted by objects within the field-of-view of the image intensifier. Image intensifiers may amplify incident photons in one or more human-visible electromagnetic wavelengths (e.g., incident electromagnetic energy in the visible spectrum between 390 nanometers and 700 nanometers) and/or one or more human-invisible electromagnetic wavelengths (e.g., the infrared electromagnetic spectrum above 700 nanometers or the ultraviolet electromagnetic spectrum below 390 nanometers).
An image intensifier typically includes a photocathode to generate photo-electrons, an electron multiplier such as a microchannel plate to generate secondary electrons, and a phosphor screen to convert the secondary electrons to photons at a human-visible wavelength. Typically, a first voltage differential is maintained between the photocathode and the microchannel plate to create a first electric field in the vacuum between the photocathode and the microchannel plate. The first electric field assists the departure of the photo-electrons from the photocathode and i.e., accelerates the photo-electrons as they travel toward the microchannel plate. A second voltage differential is maintained across the microchannel plate (i.e., the inlet side of the microchannel plate is at a different voltage than the outlet side of the microchannel plate). A third voltage differential between the microchannel plate and the phosphor screen creates a third electric field in the vacuum between the microchannel plate and the phosphor screen. The third electric field assists in the departure of the secondary electrons from the microchannel plate and accelerates the secondary electrons toward the phosphor screen.
Image intensifiers operate by collecting or capturing existing light photons using a simple or compound objective lens array. The source of the existing light photons may be naturally occurring (e.g., starlight, moonlight) or artificially generated (e.g., street lights, defined wavelength illuminators). Existing light photons enter the image intensifier through the objective lens array and strike the photocathode. The photocathode converts the incident existing light photons to photo-electrons that are accelerated through the first electric field.
The microchannel plate contains a large number of small channels that penetrate completely through the microchannel plate. Several secondary electrons are generated when a photo-electron enters a channel and impacts an internal wall of the channel. The second voltage differential across the microchannel plate accelerates the secondary electrons generated by the impact of the photo-electron with the channel wall. The accelerated secondary electrons impact the channel wall, generating a cascade of additional secondary electrons. Thus, one incident photoelectron may cause the generation of hundreds or even thousands of additional secondary electrons which exit the microchannel plate.
The secondary electrons exiting the microchannel plate accelerate through the third electric field and impact the phosphor screen. The impact of a large number of secondary electrons on the phosphor screen causes the phosphor screen to glow, providing an intensified image visible to the human eye.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications and variations thereof will be apparent to those skilled in the art.